Walkouts called by German and Belgian unions accounted for many of the cancelations, with strikes also called in Sweden and Ireland.

The airline said that over 2,000 flights, or 85 percent of its schedule, would operate as normal and that the majority of passengers affected have been re-booked on other Ryanair services.

German pilot representatives had said this week they were joining the strike action with a 24-hour walkout, ending at 2.59 a.m. Saturday, because they want pay and work conditions comparable to those at Ryanair's competitors.

The company has pointed to recent pay increases and invitations to meet for negotiations. Ryanair urged the unions "to continue negotiations instead of calling any more unjustified strikes."

Ryanair built its low-cost business model without unions, but said last year it would recognize them. Labor representatives are seeking collective-bargaining agreements in the different countries.

The airline has already been hit with strikes by flight attendants in Spain, Portugal and Belgium. Irish pilots have held four strike days.

In the Netherlands, the carrier was using non-striking pilots to keep its service running for passengers. In a tweet Thursday night, the company said that "there will be no cancellations" as a result of the Dutch union's strike.

Ryanair launched unsuccessful legal action in a Dutch court to prevent the strike in the Netherlands.

In Sweden, some 40 Ryanair pilots walked out to demand a collective labor agreement.

Martin Lindgren, head of the Swedish Air Line Pilots Association, said that "a strike is necessary to show the airline that it no longer can avoid treating its employees in a dignified manner."

At Ryanair's main Belgian hub, the Charleroi airport south of Brussels, a few dozen striking pilots gathered in the main terminal behind a banner marked "Ryanair on strike, Ryanair must change."

The Belgian Cockpit Association's Alain Vanalderweireldt said the strike in Belgium "is the conclusion of six months of discussions between Ryanair and the union representatives that has led to nowhere concretely."

While the union wants to apply Belgian labor laws to employees, Ryanair is still applying Irish laws, he said.